Field of the Invention
This invention relates to the production of cooled and cleaned gaseous mixtures comprising H.sub.2 +CO by the partial oxidation of liquid hydrocarbonaceous and/or solid carbonaceous fuel. More particularly, it pertains to a partial oxidation process for the production of synthesis gas in which water is used to quench cool and scrub the hot raw effluent stream of synthesis gas from the free-flowing refractory lined partial oxidation reaction zone, and said water is upgraded and recycled.
The partial oxidation of a carbonaceous fuel with a free-oxygen containing gas, in a free flow, non-catalytic synthesis gas generator at a temperature in the range from about 1800.degree. F. to about 3000.degree. F., and a pressure in the range from about 1 to about 250 atmospheres, produces a hot raw stream of gases comprising H.sub.2, CO and mixtures thereof. Depending on the actual composition, this gas stream is referred to as synthesis gas, reducing gas, or fuel gas. The term synthesis gas pertains to gaseous mixtures substantially comprising H.sub.2 and CO for use in catalytic chemical synthesis. Reducing gas is rich in H.sub.2 and CO and defficient in H.sub.2 O and CO.sub.2. Fuel gas contains increased amount of CH.sub.4. However, whatever is said for synthesis gas hereafter, will in most instances apply to reducing gas and fuel gas. The raw effluent gas from the partial oxidation gas generator comprises a mixture of carbon monoxide (CO), hydrogen (H.sub.2), carbon dioxide (CO.sub.2), water, and minor quantities of ammonia (NH.sub.2), argon (Ar), nitrogen (N.sub. 2), methane (CH.sub.4), and some gases of environmental concern, such as hydrogen cyanide (HCN), hydrogen sulfide (H.sub.2 S) and carbonyl sulfide (COS). The quantity of these latter gases produced depends on the quantity of sulfur and nitrogen in the carbonaceous fuel used and the operating conditions of the gasifier. Gaseous carbonaceous fuels, such as natural gas and petroleum distillates, contain very little or no sulfur and nitrogen. Liquid carbonaceous fuels such as crude oil residue, organic waste materials, sewer sludge, and liquefied coal fractions; as well as solid carbonaceous fuels such as petroleum coke, subbituminous, bituminous and anthracite coal, lignite, shale and solid organic waste materials have larger quantities of sulfur and nitrogen.
In recent years, because of the decreasing availability of gaseous carbonaceous fuels, the various liquid and solid carbonaceous fuels are being used in larger quantities as feedstocks for processes for the production of synthesis gas. Liquid, and even more so, solid carbonaceous feedstocks, contain in addition to the relatively large quantities of nitrogen and sulfur, other impurities including various inorganic materials. The impurities produce not only the gas by-products previously mentioned, but they also produce nonvolatile by-products, such as insoluble fly ash, slag, and various soluble solids including halide salts.
Generally, most of the partial oxidation by-products are removed from the raw synthesis gas before it is further processed or used. Cleaning of the raw synthesis gas, which generally comprises removal of water soluble gaseous by-products is usually necessary because many of the partial oxidation by-products are air pollutants. Further, some of the by-products can damage equipment and deactivate catalysts used to further treat the synthesis gas. For instance, dissolved hydrogen cyanide can corrode the steel piping and vessels used in the processing of the synthesis gas and can deactivate oxo and oxyl catalysts.
In a coassigned U.S. Pat. No. 4,211,646, issued to C. Westbrook et al. and incorporated herein by reference, a novel effective waste water treatment process is disclosed. However, when large quantities of hydrogen cyanide are present in the waste water, large quantities of ferrous ions are required to precipitate the cyanide. Further, disposal is required of large quantities of precipitated cyanide formed in the process. If not all of the cyanide is precipitated in the chemical portion of the treatment process, the remaining cyanide ions can adversely affect the biological reactor used to further treat the waste water.
Other previously known methods of eliminating hydrogen cyanide from waste water are not completely satisfactory since either gaseous hydrogen cyanide, or some precipitate of the cyanide ion must still be disposed of. In coassigned U.S. Pat. No. 4,189,307, issued to Marion, all or part of the hydrogen cyanide containing waste water is returned to the gas generator where the partial oxygenation process therein destroys at least a portion of the hydrogen cyanide.
In U.S. Pat. No. 4,007,129, issued to Naber et al., the acid gases are removed from the raw synthesis gas by being dissolved into a salt solution which is removed and stripped to remove the dissolved hydrogen cyanide and other acid gases. The stripped acid gases must then be disposed of.
U.S. Pat. No. 3,935,188, issued to Karwat, discloses the use of an organic scrubbing agent for the removal of hydrogen cyanide from synthesis gas. After contacting the synthesis gas with the organic scrubbing agent an aqueous alkali metal or alkaline earth metal hydroxide solution is mixed with the hydrogen cyanide rich organic scrubbing agent to form the cyanide salt. The salt solution is subsequently heated to at least 150.degree. C. to thermally convert the cyanide salt to ammonia and formate.
In U.S. Pat. No. 2,989,147, issued to Gollmar, hydrogen cyanide dissolved in the waste water is removed by passing the waste water through a series of aeration towers which utilize air and carbon dioxide gas to remove the hydrogen cyanide from the waste water. However, disposal of the gaseous hydrogen cyanide is still required.